This invention relates to a thrust-action mechanical pencil in which a lead-forwarding mechanism is attached to an outer sleeve by an inner ring to prevent forward movement, and has an elastic retaining member to prevent looseness used to retract the lead-forwarding mechanism to said inner ring and a retaining sleeve to prevent rear movement of a mouth piece.
Such thrust-action mechanical pencils are commonly known, as for example, the pencil described in Japanese Utility Model publication No. 87984/59 (1984).
In this common example, an inner sleeve acting as a lead-forwarding mechanism is inserted in an outer sleeve with the inner sleeve being pressed rearward by a retaining ring set in a small groove engraved around the circumferential end of a mouth piece on the inner sleeve and an elastic member on the connecting part of the inner sleeve that presses against a receiving part for the elastic member.
The above example solves the usual problem of threaded mouth piece-typed pencils, becoming loose in use and breaking the lead and also causing the loss of the mouth piece which sometimes slips out, by attaching the lead-forwarding mechanism to the outer sleeve with a retaining ring and elastic member.
However, a problem with the above example is that it cannot be assembled in one motion. This is because separate actions are required to maintain the inner sleeve forced rearward and to insert the retaining ring by means of jig. Also because the lead-forwarding mechanism is attached to the outer sleeve by engaging the retaining ring with the small groove engraved around the circumferencial end of the mouth piece, looseness between the small groove and the retaining ring cannot be not compensated for without increasing the working accuracy of both the small groove and the retaining ring. Further there is a possibility that the retaining ring can slip out of the small groove due to the elasticity of the elastic member and jig is necessary to the set retaining ring.